Variadic function

Variadic function
You are encouraged to solve this task according to the task description, using any language you may know.

Create a function which takes in a variable number of arguments and prints each one on its own line. Also show, if possible in your language, how to call the function on a list of arguments constructed at runtime.

Variable arguments of arbitrarily typed values are not permitted in ALGOL 68.
However a flexible array of tagged types (union) is permitted. This effectively
allows the passing of strongly typed variable arguments to procedures.

Works with: ALGOL 68 version Revision 1 - no extensions to language used

An array of parameters with a count as parameter zero can be used in a subroutine to simulate a variadic function. The values in the array should probably be cleared when the subroutine returns because the array is a global variable.

An array of parameters can be passed to any function by applying the same syntax to a function-call:

args :=["Rosetta","Code","Is","Awesome!"]printAll(args*)

AutoHotkey Basic (deprecated):

Function arguments can be given default values. Comparison with "" can indicate that an argument was present (and not of value ""). As of version 1.0.48, you can pass more parameters than defined by a function, in which case the parameters are evaluated but discarded. Versions earlier than that produce warnings.

AWK allows to call functions with fewer than the defined arguments; the missing one(s) default to "". Comparison with "" can check if the argument was present (and not of value ""). To call a function with more than the defined arguments, this produces a warning.

Functions like f() can take only a few arguments. To accept more arguments, or to accept "" as an argument, the function must take an array, and the caller must bundle its arguments into an array. This g() accepts 0 or more arguments in an array.

Variadic functions on FreeBASIC are somewhat similar to those in C.
The parameter list does not pass information about parameter type. If necessary, the type information has to be passed for example in the first parameter.
C calling convention has to be used (with keyword cdecl).

Beta BASIC uses keyword DATA to specify variable parameter list.
The parameters are read with READ command just like when reading conventional DATA statements.
The existence of more parameters as well as the type of each parameter can be checked with function ITEM().

The ANSI C standard header stdarg.h defines macros for low-level access to the parameter stack. It does not know the number or types of these parameters; this is specified by the required initial parameter(s). For example, it could be a simple count, a terminating NULL, or a more complicated parameter specification like a printf() format string.

In C, there is no way to call a variadic function on a list of arguments constructed at runtime.

However, all standard library functions which are variadic have a corresponding version, usually named by prepending the letter "v", that is non-variadic and takes a va_list as argument in place of the variadic arguments. For example, printf has a corresponding vprintf which takes a format string and a va_list value as arguments.

Nevertheless, the only way of obtaining a va_list is from a variadic function itself. So the "v" functions are only useful for writing a variadic function "wrapper" that performs some processing and then calls on one of the "v" functions with its va_list. C still provides no standard way to construct a va_list manually at runtime.

The actual implementation of va_list is implementation-dependent. If you are developing on a specific platform, you may use platform-specific knowledge to create a va_list by hand in a non-portable way. For example, on many platforms, a va_list is simply a pointer to a buffer where the arguments are arranged contiguously in memory.

The C++ varargs are basically the same as in C (therefore you can just take the code from C), but there are some limitations:

Only PODs (basically, every type you could also write in C) can be passed to varargs

An important difference is that enums are distinct types with possibly different representation than int in C++, but enumeration values are still converted to int when passed to varargs. Therefore they have to be accessed as int in va_arg.

C++11 in addition allows typesafe variadic arguments through variadic templates. Some compilers, such as gcc, already provide this functionality. The following implements the task with variadic templates:

Variadic functions in the Déjà Vu standard library generally end with (, [ or {. For this purpose, ), ] and } are autonyms (that is, they have a global bindings to themselves, so that ) is the same as :)).

Words taking variable numbers of arguments may be written by specifying the number of parameters to operate upon as the top parameter. There are two standard words which operate this way: PICK and ROLL.

: sum ( x_1 ... x_n n -- sum ) 1 ?do + loop ;4 3 2 1 4 sum . \ 10

Alternatively, you can operate upon the entire parameter stack for debugging by using the word DEPTH, which returns the number of items currently on the stack.

Fortran has no varargs for subroutines and functions, but has optional arguments and varargs functions can be programmed passing an array as argument. Moreover you can program elemental functions or subroutines, i.e. function acting on a single element but which can be used automatically over a vector (but there are limits to respect in order to make it possible, e.g. it is not possible to use print)

The following code shows how an optional vector argument can be used to pass a variable number of argument to a subroutine.

There are two types of variadic mechanisms supported in Go, both specified by using a ... before the name of the last argument in the function parameter list. [1]

If you know that all the variadic arguments are going to be of a certain type, then you can declare that type after the ..., and all the variadic arguments will be collected in a slice variable, for example:

func printAll(things ...string){// it's as if you declared "things" as a []string, containing all the argumentsfor _, x :=range things { fmt.Println(x)}}

On the other hand, if you want to be able to take different types of variadic arguments (like Printf does), you can omit the type. What happens is that the compile-time type of the variable that collects it is "interface{}" (the universal interface, i.e. it gives you no information); but the runtime type of the variable will be a struct whose fields contain the arguments and their proper types. You must use reflection (via the reflect module) to obtain these types and values. Because this is ugly, it is not shown here.

If you wish to supply an argument list to a variadic function at runtime, you can do this by adding a ...after a slice argument:

So here we created a type class specially for the use of this variable-argument function. The type class specifies a function, which takes as an argument some kind of accumulated state of the arguments so far, and returns the type of the type class. Here I chose to accumulate a list of the string representations of each of the arguments; this is not the only way to do it; for example, you could choose to print them directly and just accumulate the IO monad.

We need two kinds of instances of this type class. There is the "base case" instance, which has the type that can be thought of as the "return type" of the vararg function. It describes what to do when we are "done" with our arguments. Here we just take the accumulated list of strings and print them, one per line. (We actually wanted to use "IO ()" instead of "IO a"; but since you can't instance just a specialization like "IO ()", we used "IO a" but return "undefined" to make sure nobody uses it.) You can have multiple base case instances; for example, you might want an instances that returns the result as a string instead of printing it. This is how "printf" in Haskell can either print to stdout or print to string (like sprintf in other languages), depending on the type of its context.

The other kind of instance is the "recursive case". It describes what happens when you come across an argument. Here we simply append its string representation to the end of our previous "accumulated state", and then pass that state onto the next iteration. Make sure to specify the requirements of the types of the arguments; here I just required that each argument be an instance of Show (so you can use "show" to get the string representation), but it might be different for you.

That said, J expects that members of lists all use the same kind of machine representation. If you want both character literals and numbers for arguments, or if you want arrays with different dimensions, each argument must be put into a box, and the function is responsible for dealing with the packing material.

In some rare cases, you may want to pass an array as just a single argument, but doing it directly would expand it to be the entire argument. In this case, you need to cast the array to Object (all arrays are objects) so the compiler doesn't know it's an array anymore.

A Lasso method parameter name can prefixed by "..." to specify a variable number of parameters, which are made available as a staticarray. If no name is specified, the staticarray will be named "rest".

define printArgs(...items) => stdoutnl(#items)define printEachArg(...) => with i in #rest do stdoutnl(#i)

printArgs('a', 2, (:3))printEachArg('a', 2, (:3))

To expand an existing list, pass it to the method using invocation syntax.

In MATLAB, the keyword "varargin" in the argument list of a function denotes that function as a variadic function. This keyword must come last in the list of arguments. "varargin" is actually a cell-array that assigns a comma separated list of input arguments as elements in the list. You can access each of these elements like you would any normal cell array.

Variable number of arguments to a macro can be done using the text keyword identifying the kind of argument to the macro. In this way, each argument can be of any kind (here, as example, I show all the primitive types that Metafont knows)

Objective-C uses the same varargs functionality as C. Like C, it has no way of knowing the number or types of the arguments. When the arguments are all objects, the convention is that, if the number of arguments is undetermined, then the list must be "terminated" with nil. Functions that follow this convention include the constructors of data structures that take an undetermined number of elements, like [NSArray arrayWithObjects:...].

Since lists are flattened when placed in a list context, you can just pass an array in as an argument and all its elements will become separate arguments:

@args=("Rosetta","Code","Is","Awesome!");print_all(@args);

Introduced experimentally in 5.20.0, subroutines can have signatures when the feature is turned on:

use5.020;use experimental 'signatures';

Perl policy states that all bets are off with experimental features—their behavior is subject to change at any time, and they may even be removed completely (this feature will most likely stay in, but expect changes in the future that will break any scripts written using it as it stands in 5.20.1).

If a subroutine has no formal parameters but mentions the variables @_ or %_ in its body, it will accept arbitrary positional or keyword arguments, respectively. You can even use both in the same function.

sub foo {.sayfor@_;say.key,': ',.valuefor%_;}

foo 1,2, command =>'buckle my shoe',3,4, order =>'knock at the door';

This prints:

1
2
3
4
command: buckle my shoe
order: knock at the door

Perl 6 also supports slurpy arrays and hashes, which are formal parameters that consume extra positional and keyword arguments like @_ and %_. You can make a parameter slurpy with the * twigil. This implementation of &foo works just like the last:

The Prolog standard does not require support for variadic functions,
but there is no need for them in Prolog, because Prolog has first-class support for terms, including lists and terms such as (1,2,3), which are also
known as comma-lists.

For example, the standard predicate write/1 has just one formal
argument, but it will accept any term. Thus, except for the
additional parentheses, write/1 is like a variadic function that
requires at least one argument:

?- write( (1) ), nl.
1
?- write( (1,2,3) ), nl.
1,2,3

In practice, since the minimum length of a comma-list is 2, Prolog
lists are often used instead of comma-lists to handle situations where
vararg-behavior is wanted. For example:

Python also has keyword arguments were you can add arbitrary func(keyword1=value1, keyword2=value2 ...) keyword-value pairs when calling a function.
This example shows both keyword arguments and positional arguments. The two calls to the function are equivalent. *alist spreads the members of the list to create positional arguments, and **adict does similar for the keyword/value pairs from the dictionary.

RapidQ uses special keywords SUBI and FUNCTIONI for procedures and functions with variable number of parameters.
Numeric parameters are accessed from array ParamVal and string parameters from array ParamStr$.

SUBI printAll (...) FOR i = 1 TO ParamValCount PRINT ParamVal(i) NEXT i FOR i = 1 TO ParamStrCount PRINT ParamStr$(i) NEXT iEND SUBI

Note that if you define the function anonymously using lambda, and you want all the args to be collected in one list (i.e. you have no parameters before the parameter that collects everything), then you can just replace the parentheses altogether with that parameter, as if to say, let this be the argument list:

f is defined as a function that takes a list of any length of items of any type, and uses a built-in heuristic to decide how to print them. All functions in the language are polymorphic and variadic unless specifically restricted to the contrary.

Each method can have a variable-length parameter (VPL), indicated by empty brackets after the parameter name. The VLP (if present) will be replaced with an array containing all the extra arguments passed to the method. Effectively, extra arguments are absorbed into the array. Calling the function with fewer parameters than needed is still a runtime error. The VPL may be omitted, which will result in an empty array as the value of that parameter.